This invention relates to a video endoscopic system having an electrosurgical capability and, in particular, to an electromagnetic electrostatic shield method that prevents high frequency current and voltage from adversely affecting the video section of the instrument.
As explained in greater detail in reissued U.S. Pat. Nos. Re. 31,289 and Re. 31,290 to Moore et al, endoscopes can now be equipped with small video cameras that are able to be passed into confined regions that have heretofore been inaccessible to this type of viewing equipment. The heart of the camera is a small solid state image sensor, sometimes referred to as a charge coupled device (CCD), that is able to record light images of a remote target and provide video signals indicative of the target information. A similar type system is also disclosed in U.S. Pat. No. 4,074,306 to Kakinuma et al.
As is well known, an endoscope, when used in medical applications, can provide the examining physician with a visual presentation of a remote target and also can be used as a means for carrying out certain diathermic procedures. A biopsy channel is usually housed within the insertion tube of the instrument. The active lead of a high frequency generator is passed into the viewing region of the instrument. In practice, the tissue to be treated is placed between an electrode carried at the distal end of the active lead and a plate placed against the skin of the patient near the treated area. A high frequency current is then passed through the electrode to either heat coagulate and/or cut the tissue under treatment.
When a current is passed through the human body, it will affect the myocardium by stimulating the heart muscles. Low frequency current passing through the heart muscle can cause ventricular fibrillation which oftentimes leads to death. Frequencies above 300 kH.sub.z, however, are found to have little affect on the myocardium and radio frequency currents are therefore universally used in electrosurgery of this nature. High frequency signals, however, can leak via distributed capacitance and electromagnetic and electrostatic coupling to other parts of the instrument and therefore pose a danger to both the patient and the examining physician. Precautions must be taken to prevent such leakage to exposed surfaces of the instrument that might come in contact with either person.
With the advent of video equipped endoscopes, high frequency electrosurgical generators have also been found to adversely affect the operation of the video section of the instrument. Radio frequency alternating current will flow through the stray capacitance between the active lead of the electrosurgery generator and the video and other service leads passing along the insertion tube as well as the image sensor assembly itself. High frequency alternating current will also be induced into these leads and assemblies by the electromagnetic and electrostatic fields generated by the high frequency electrosurgery current and voltage.